| Two Asian carp species, the bighead carp (Hypopthalmichthys nobilis) and silver carp (H. molitrix), have invaded much of the Mississippi River basin. However, it is unclear whether these species are able to successfully reproduce in navigation pools of the Upper Mississippi River (UMR) relative to the unimpounded lower reaches. I compared the reproductive output of Asian carp between the pooled UMR and unpooled Middle Mississippi River (MMR) by quantifying larval densities and inferring survival to the juvenile stage. During May through August of 2005 and 2006, larvae were sampled from the MMR and UMR Pools 26, 24, 22, and 20 using a 1m X 2m neuston net. Juveniles were sampled by seining in backwater sites in each of the UMR pools and in the MMR from July through September of 2005 and 2006. A total of 582 larval samples was collected with larval Asian carp occurring in only 25 samples. All larval Asian carp were collected in the MMR and Pool 26 in 2005 and 99.9% of larval Asian carp were collected in the MMR and Pool 26 in 2006. Peak density was greater in the MMR than in Pool 26 (t=2.50, P=0.05, df=6), and spawn duration was longer in the MMR than in Pool 26 (Ksa=2.09, P<0.001). Larval production occurred with high or rising discharge after water temperatures reached 18 °C. Sites that contained high densities of larval Asian carp (MMR and Pool 26) also contained juvenile Asian carp. All juvenile Asian carp were collected in the MMR in 2005 and 97% of juveniles were collected in the MMR in 2006. No juveniles occurred in Pools 24, 22, or 20. Current water level management in the UMR may limit larval production of Asian carp and subsequent recruitment to the juvenile stage during dry years. By targeting the mechanism of population growth (i.e., reproduction), managers can influence the establishment and subsequent dispersal of Asian carp. |